Foundry processes and products

ABSTRACT

THE OVERALL STRENGTH OF FOUNDRY CORES AND MOLDS AND PARTICULARLY THE STRENGTH OF THE CORES AND MOLDS AT HIGH RELATIVE HUMIDITY CONDITIONS ARE IMPROVED BY TREATING THE FOUNDRY SAND WITH AN AQUEOUS SOLUTION OF AN INORGANIC OR ORGANIC ACID AND WASHING THE SAND WITH WATER BEFORE THE SAND IS COMBINED WITH A FOUNDRY BINDER CONTAINING A SILANE COMPOUND HAVING THE FORMULA   R-SI(-O-R&#39;&#39;)2-R&#34;   WHEREIN R IS AN ORGANIC RADICAL, R&#39;&#39; IS ALKYL AND R&#34; IS -OR&#39;&#39; OR ALKYL.

sates Patent Office 3,745,139 Patented July 10, 1973 3,745,139 FOUNDRY PROCESSES AND PRODUCTS Victor Kachur, Bloomington, and Richard H. Toeniskoetter, Edina, Minn., assignors to Ashland Oil Inc., Houston, Tex. No Drawing. Filed May 3, 1971, Ser. No. 139,907 Int. Cl. C08g 51/04 US. Cl. 260-38 10 Claims ABSTRACT OF THE DISCLOSURE The overall strength of foundry cores and molds and particularly the strength of the cores and molds at high relative humidity conditions are improved by treating the foundry sand with an aqueous solution of an inorganic or organic acid and washing the sand with water before the sand is combined with a foundry binder containing a silane compound having the formula wherein R is an organic radical, R is alkyl and R" is ---OR or alkyl.

BACKGROUND It is well known in the art that one can impart general improved strengths and increased humidity resistance to foundry cores by adding a silane compound to the resinous foundry binder used to form the cores. Foundry cores made with such resinous binders as phenolic/isocyanate systems, furan systems, oil modified polyol/polyisocyanate systems, phenolic resins and urea/phenolic resins have a tendency to lose strength and become weak upon exposure to humid conditions. As illustrated by U.'S. Pats. 3,409,579 and 3,403,721, silane compounds have been added to such resinous binders to increase the humidity resistance and general strength of foundry cores made with these binders. Aqueous dispersions of silane compounds have also been used as binders themselves (see US. Pat. No. 3,093,494).

Foundry sands are conventionally prepared for use by cleaning and sizing by air flotation and are generally cleaned and prepared by washing with water which may or may not contain an amine flotation agent. The sands are commercially supplied to the foundry in a dry form ready for mixing with the binders and shaping in the patterns. The prior art indicates that in some instances foundry sand may contain various impurities, such as iron oxide (US. Pat. 3,525,379,) and in some instances the foundry sand produces superior cores if it is used in an unwashed or uncleaned condition (US Pat. 3,135,029). Still other prior art indicates that such cleaning and washing is desirable (U.S. Pats. 2,765,506 and 3,007,893 None of the prior art indicates how the general strength or humidity resistance of foundry cores can be improved other than by the addition of silane compounds to the foundry binder.

Objects of this invention are, therefore, to increase core strength in general, to increase the humidity resistance of foundry cores, to increase the effectiveness of silane compounds, to provide an inexpensive method for increasing the effectiveness of silane compounds, to provide an inexpensive method for increasing general strength and humidity resistance of foundry cores which does not interrupt normal foundry sand operations, and to achieve other objects which will become apparent from this disclosure.

SUMMARY OF THE INVENTION The present invention increases the general strength of foundry cores prepared with a resinous binder which contains a silane compound. While not wishing to be bound by theory, it is believed this improved strength results from this invention increasing the effectiveness of the silane compound added to the binder. It has been found that this invention particularly improves the humidity resistance of foundry cores.

As used in this disclosure, cores means both cores and molds and humidity" means moisture in gaseous, liquid, spray or other forms.

In general this invention comprises treatment of the foundry sand by contacting the foundry sand with an aqueous solution of an inorganic or organic acid, removing excess solution from the sand, washing the sand with water to remove substantially all of the acid, and drying the sand to return the moisture content to a level acceptable for general foundry use. The sand treatment provided by this invention does not interfere with or alter the conventional method of sand supply to the foundry since the sand may be treated according to this invention in a continuous operation, i.e., while the sand is being processed for cleaning and sizing, or the sand may be treated in a batch operation, i.e., while the sand is in storage, and since treatment according to the present invention leaves the sand dry and ready for use by the foundry.

The foundry sands useful in the present invention are conventional foundry sands such as silica sands having a high silica content, for example a silica content of at least by weight. Examples of such foundry sands are (1) white silica sands such as Wedron White Silica sand, (99.8% by weight silica), Ottawa White Silica sand (99.8% silica), Minnesota White Silica sand (98.5% silica); (2) lake sands, such as Port Crescent sand (95.0% silica), Manley 20KK sand (91.9% silica), Nugent Lake sand (94.2% silica), Lake Shore sand (93.5% silica); and (3) bank sands such as Juniada Bank sand (90.2% silica). These foundry sands normally have a Grain Fineness Number (GFN) of about 50 to 90, as determined by the standard AFS method.

It has been found that this invention provides the greatest improvement in core strength when the lower silica content sands are involved, such as the lake or bank sands. Conversely, this invention provides a lesser increase in core strength when the sands having a high silica content are involved.

The inorganic acids useful in this invention are aqueous solutions of such inorganic acids as hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, chromic acid, and mixtures thereof. The organic acids useful in this invention are aqueous solutions of such organic acids as p-toluene sulfonic acid (p-TSA), phenol sulfonic acid, trichloro acetic acid, oxalic acid, and mixtures thereof. These acids are generally employed in concentrations of between about 1% and about 30% by Weight based on the weight of the acid solution. The concentration is preferably between about 5% and about 20% and most preferably in the range of about 10%. The particular concentration used, of course, will depend upon the soaking time, the sand involved, the particular acid used, as well as other factors. For continuous treatment with short contact times, high concentrations may be necessary. Conversely, if the sand is contacted with the acid during storage thus producing long contact times, lower concentrations of acid may be used.

The foundry sand is treated according to this invention by contacting the sand with an aqueous solution of the acid. The sand is usually soaked or dipped in the acid solution but the solution may be sprayed onto the sand or otherwise contacted. The sand and acid solution may be contacted at any temperature convenient in the particular operation in use. Room temperature is convenient but other temperatures are suitable, for example, hot or cold sand may be immersed in a boiling acid solution. A higher temperature may be used to reduce the contact time required. After the sand is subjected to the above contacting 5 with the acid solution, the acid solution is drained or otherwise removed from the sand thus removing the excess acid from the sand. The sand is then washed with water to remove substantially all of the remaining acid and dried in a conventional manner. One water wash is usually sufiicient to remove the acid, but two or more may be used if necessary or desired. In general the pH of the sand should be returned to at least 5 and preferably to between 6 and 7 for foundry use. The drying is generally performed at between about 150 and about 500 F. The drying temperature and time will of course depend on the equipment used for a given amount of sand. The sand normally must be dried to a moisture content of less than about 1% by weight and in general a moisture content of 0.1% may be used.

The silane compounds useful in this invention have the general formula R-Si one of in which R is as defined above, Y is alkylene and the alkyl, alkenyl and alkylene groups contain from 1 to 6 carbon atoms. Specific examples of such silane compounds are In general, any silane having the above general formula gives satisfactory results in this invention but a particular silane may give superior results with a particular resinous binder. The silane compound is generally added to the foundry binder in amounts of between about 0.05 and 1.0% by weight based on the weight of the binder. Preferably the amount of silane compound should be between about 0.1 and 0.5% with about 0.25% being the most preferred amount.

The resinous binders useful in this invention are the foundry binders which when used with the above silane compounds show improved strength or resistance to humidity in the foundry core. Generally these foundry binders are the phenolic/polyisocyanate binder systems such as described in U.S. Pat. 3,409,579; furan binder systems such as described in U.S. Pat. 3,346,534; oil modified polyol/polyisocyanate binder systems such as described in U.S. Pat. 3,255,500; and phenolic and urea/ phenolic resin binder systems such as described in U.S. Pats. 3,404,198 and 3,306,864.

The binder composition containing the silane compound is generally mixed with the foundry sand in amounts of about 0.25 to about 10% by weight based on the weight of the foundry sand. Normally the binder composition is used in an amount between about 1.0 and about 5.0%.

This invention finds particular utility in operations where foundry cores are dipped, sprayed or otherwise coated with an aqueous core wash composition. The aque ous core wash solution causes the cores to lose considerable strength because of the moisture absorbed by the core. Normally the cores are baked to dry them after the aqueous core wash solution is applied to lower the moisture content to an acceptable level for casting. The baking normally causes an even further loss of strength. This invention provides for a substantial reduction in the amount of strength lost by cores in operations utilizing aqueous core washes.

Further details and other advantages of this invention will be apparent from the following examples, which are illustrative of the practice of this invention.

Examples 1-13 In these examples the given sand is soaked, washed and dried as specified. In all runs the sand has a moisture content below 1.0% by weight of the sand when the test cores are made. The phenolic resin used is obtained by charging 1014 g. of phenol, 720 g. of paraformaldehyde in flake form, 15 g. lead naphthenate (24% solution) and 120 ml. benzene to a reflux system and heating to about C. and refluxing at that temperature for 6 hours. During this time water and benzene are distilled off. During reflux 100 ml. of benzene are added. A total of 298 mls. of water was distilled over. The resin was found to be a benzylic ether type of phenolic resin (see U.S. Pat. 3,409,579). Fifty parts by weight of the resin is then blended with 30 parts furfuryl alcohol and 20 gxf aromatic solvent having a boiling range of 315 to The polyisocyanate is a commercially available product, which is a mixture of diand tri-isocyanate (e.g., mondur M-R"). The phenolic and polyisocyanate components are used in a 1:1 ratio and an organic solvent, butyl acetate, was employed in an amount of about 50% by weight based on the weight of the phenolic/polyisocyanate binder. The silane compound when used is and iS used at by weight based on the weight of the binder composition.

In each run 5000 parts by weight of sand is mixed with 100 parts of phenolic/polyisocyanate binder in a Hobart Model A- paddle mixer at speed #2 until the binder composition is evenly distributed on the sand particles. Mixing time is about 4 minutes. The sand/ binder mix is then blown under 100 p.s.i.g. air pressure into standard 65 cc. dogbone patterns (ASTM No. C- or Standard AFS Tensile Test Method) and cured by gassing the dogbone core witha gaseous mixture of nitrogen (carrier gas) and triethyl amine (catalyst) under 60 p.s.i.g. followed by purging the core with air. The nitrogen/triethyl amine mixture is obtained by bubbling the nitrogen through liquid triethyl amine. There are three dogbone cores made in each run and exposed to the specified humidity for 24 hours. The tensile strength values given below represent the average tensile 6 strength of the three dogbone cores of each run after TABLE VI exposure to the specified humldlty. weldron sand untreatei TABLE I Silane in the binder.

Port Crescent sand, untreated. Silane in the binder. figfigg; 3333 (percent) (p.s.i.)

Relative Tensile humidity strength (percent) (p.s.i.) 80 280 30 310 92 150 50 280 100 100 3% $8 100 m TABLE VII Weldron sand soaked in 10% HCl for 72 hours, washed TABLE H with water and dried as m Table II.

Silane in the binder. Port Crescent sand, soaked in water for 24 hours and dried 18 hours at 260 F. and 1 hour at 425 F. mg); $3322 3 Silane in the binder. 20 (percent) (p.s.i.)

Relative Tensile humidity strength (percent) (p.s.i.)

TABLE VIII Port Crescent sand soaked in 10% HCl for 24 hours, washed with water and dried 24 hours at 425 F.

TABLE 111 Percent Relative Tensile silane in humidity strength Port Crescent sand, soaked in 10% HCl for 72 hours, binder (p (p-swashed with water and dried as in Table I I. 0 m 340 Sdane 1n the blnder. M 50 380 0.2 so 420 0.3 so 430 0.5 50 400 0 92 110 0.1 92 260 8'2 8% 328 015 92 330 o 100 130 0.1 100 190 0.2 100 230 0.3 100 240 0.5 100 300 TABLE IV TABLE IX Port Crescent sand soaked in HCl for 24 hours, Port Crescent sand soaked in 10% H 80 for 24 hours, washed with water and dr e as 111 Table washed with water and dried as in Table II. Silane in S1lane in the binder. binders.

Relative Tensile h ii i d i Tensile humidity strength t t th l (percent; f s i. (P (D-SJJ is 550 ,3 28 50 430 20 20 500 5 so 360 3% 23 53 3% 338 0 s 100 230 TABLE X 10 100 240 I 20 100 280 Port Crescent sand soaked in H PO for 24 hours, washed with water and dried 24 hours at 450 F. Silane T v in binder.

Percent Relative Tensile Port Crescent sand soaked 1n l0% HCl for 5 minutes, M H, PO humidity strength washed WlIh water and dried as 1n Table II. (percent) (p s i.)

Silane in the binder.

1 19 500 a 18 500 Relative Tensile 10 18 490 ltumidittyg stfengfl)! 2(1) GI'CBH .S.

p p a 92 420 10 92 380 20 92 440 1 100 220 5 100 230 10 100 290 20 100 320 7 TABLE x1 Port Crescent sand soaked in 17% H 80 for 7 days, washed with water and dried 24 hours at 450 F.

Percent Relative Tensile silane in humidity strength binder (percent) (p.s.i.)

TABLE XII Port Crescent sand soaked in p-toluene sulfonic acid overnight and washed with water. Dried at 425 F. for 16 hours.

Relative Tensile strength (p.s.i.) Percent humidity Cores prepared as in Table XII are dipped in a conventional core wash composition which is an aqueous solution or suspension of silica and graphite. The cores are then baked at 425 F. for 1 hour and the tensile strength determined after the cores are cooled to room temperature. The control cores are baked but not dipped.

Percent p-TSA Silane Dipped Control Example 14 This example is an extreme test to illustrate the improved strength this invention provides for cores which are dipped in aqueous solutions, such as core wash compositions. The same binder, silane, and test methods are the same as in Examples 1-13.

TABLE XIV This treated sand is soaked overnight in 10% H PO washed in water and dried. The cores are stored for 5 days and at ambient conditions after removal from the core box then immersed in boiling water for 24 hours. The tensile strengths are:

Untreated Untreated Treated Treated Sand no silane with silane no silane with silane Port crescent. '0 52 0 203 Wedron '0 45 '0 330 Cores are barely handleable.

Example In this example the binder is a hot-box furan binder prepared by mixing 37.3 parts furfuryl alcohol, 51.5 parts urea/formaldehyde concentrate (25% by weight urea; 60% formaldehyde and 15% water), and 11.2 parts urea and heating to 210 F. over a period of 4.25 hours. The pH is maintained at 5.6. The mixture is held at that temperature for an additional 0.25 hour then neutralized. Water is then stripped from the mixture to obtain a viscosity of about 6.0 stokes.

Eighty-three parts of the above binder and l7 parts of a solution containing 44.9% by weight water, 14.1% ammonium chloride and 41.0% urea are mixed with 5000 parts of sand. The sand/ binder mixer is rammed into a 450 F. core box and held for a core box dwell time of 60 seconds then removed from the core box. In the table below all tensile strengths are determined after the cores were cooled to room temperature except the hot core strength, which is the core strength within one minute after removal from the hot core box.

The sand when treated is soaked overnight in 10% H washed with water and dried at 425 F. overnight. The silane when used is the same as in Examples 1-13 and is present in an amount 0.25% by weight based on the weight of the total binder used.

No With No With silane silane silane silane Condition 7.. F 8 Dip then bake 425 F.

In runs 26 the cores are exposed to the specified relative humidity for 24 hours. In runs 7 and 8 the cores are baked for 24 hours. In run 8 the cores are dipped in an aqueous silica/graphite core wash.

Example 16 Example 15 is repeated except the binder is a no-bake binder which contains 108 parts by weight of an oilmodified alkyd resin having a hydroxyl number of about (prepared from 64.5% linseed oil, 14.4% pentaerythritol, and 21% isophthalic acid), 50 parts xylene, 10 parts sodium perborate, 7.5 parts of a 6% cobalt naphthenate solution and 42 parts of a mixture of crude diand tri-phenylmethane-diand tri-isocyanate (commercially available as Mondur MR). This binder is mixed with 10,000 parts Port Crescent sand and the cores cured at room temperature. The amount of silane when used is 0.25% by weight based on the alkyd.

No With No With silane silane silane silane Run Condition REL.-. e 425 F.. -4 Dip then bake 425 F.-

Example 17 Example 3' (Table III) is repeated except the silane is as follows:

9 The resulting tensile strengths for each of these runs are comparable to those in Example 3.

We claim:

1. A method of producing a foundry core or mold having improved strength and humidity resistance, which comprises:

contacting foundry sand with an aqueous solution of an inorganic or organic acid having a concentration between about 1% and about 30% based on the weight of the acid solution;

washing the foundry sand with water to bring the pH of the sand up to at least drying the foundry sand; forming a mixture of the dried foundry sand, a resinous foundry binder, and a silane compound having the general formula RSi wherein R" is OR or an alkyl radical of 1 to 6 carbon atoms; R is an alkyl radical of 1 to 6 carbon atoms; and R is alkyl, haloalky, alkenyl, aryl mercaptoalky, or one of:

in which R is as defined above, Y is alkylene and the alkyl, alkenyl, and alkylene groups contain from 1 to 6 carbon atoms; shaping the sand/binder/silane mix; and curing the binder. 2. A method according to claim 1 wherein the acid is an inorganic acid.

3. A method according to claim 2 wherein the acid is HCl, H 80 H PO or chromic acid.

4. A method according to claim 1 wherein the acid is an organic acid.

5. A method according to claim 4 wherein the acid is ptoluene sulfonic acid.

6. A method according to claim 1 wherein the acid concentration in the aqueous solution is between about 5% and about 20% by weight.

7. A foundry mix prepared by mixing (a) foundry sand which has been contacted with an aqueous solution of an inorganic or organic acid having a concentration between about 1% and about 30% based on the weight of the acid solution,

5 washed with water to bring the pH of the sand up to at least 5 and dried; (b) a resinous foundry binder; and (c) a silane compound having the general formula RSi wherein R" is OR or an alkyl radical of 1 to 6 carbon atoms; R is an alkyl radical of 1 to 6 carbon atoms; and R is alkyl, haloalkyl, alkenyl, aryl, mercaptoalkyl, or one of:

NH Y

NHgYNHY- C z -CHYOY ROOCYNHYNHY- RCOOY in which R is as defined above, Y is alkylene and the alkyl, alkenyl, and alkylene groups contain from 1 to 6 carbon atoms; 8. A foundry mix according to claim 7 wherein the foundry sand has been contacted with an inorganic acid. 9. A foundry mix according to claim 7 wherein the foundry sand has been contacted with an organic acid. 10. A foundry core or mold produced by the method of claim 1.

References Cited UNITED STATES PATENTS 3,184,814 5/1965 Brown 164-43 3,227,564 1/1966 Standen 16443 3,403,721 10/1968 Robins et a1. 164-43 LEWIS T. JACOBS, Primary Examiner U.S. Cl. X.R.

260-37 N, 41 A, DIG. 40 

